Garrrr 2 more Cracking Blades!

C

Comanche14

Joined
Aug 12, 2005
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26
I've hardened two blades and differently heat treated them but after the heat treat they are full of cracks where the heat was applied!:grumpy: Does anyone know what im doing wrong?
 
Could be overheating during forging, not normalizing or just not holding your mouth right. :) What kind of steel and quench medium are you using?
 
There both made out of a leaf spring and one was quenched in oil while the other was quenched in water. I'm quenching the blade after tempering it would that cause problems cos they seemed ok before i did that?
 
Quenching after tempering is unnecessary but it wouldn't cause any problems.
 
1. Don't use water

2. Preheat your oil to about 130-140 F (heat up a piece of scrap steel and dunk it in the oil)

3. Let the blade cool after the quench to where you are just able to handle it.

4. Temper at 350F or so for a leaf spring....then let it cool on its own.
 
What kind of music are you listening to while you quench? Hoe thin is the edge? Other posts talk about how thin before they crack.
Cheers Ron
 
Yeah, I've found that having any of the Beach Boys songs playing while doing the heat treat is beneficial.....either that, or "Tequila" by the Champs.
 
Thanks for the info Greg! I was listening to the ABC Golden Oldies maybe that isn't so good? I think i'll have to dig up a Beach boys album from out of the old mans music dungeon!:D
 
Comanche14 said:
I've hardened two blades and differently heat treated them but after the heat treat they are full of cracks where the heat was applied!:grumpy: Does anyone know what im doing wrong?
Click to expand...


I agree about oil rather than water. Also about too thin on the edge. Are you normalizing/stress relieving before hardening? Bring the piece up to about 25 degrees above quench temperature and allow to cool in still air until black. Do this at least once - some makers do it up to three times. The idea is to take the stresses out of the metal and to restore the fine grain structure.

You say "cracks where the heat was applied!" Are you heating only the edge? If so, I would heat the whole piece and quench just the edge but don't allow too much difference in temperature between the quenched edge and the rest of the blade - or at least not for long. I get the piece up to temperature, quench the edge thoroughly, then quench the rest of the piece just as it is losing color. Then get the piece _immediately_ into the tempering oven. Stresses continue to build after the quench and should be relieved by tempering as soon as possible.

You may have seen this method of edge quenching before but I'll put it here again. Make a small "table" for edge quenching. Use a scrap piece of metal (mine is about six inches long by about two inches wide). Drill and tap it so you can put a bolt in each corner. The bolts are the adjustable legs for the table. I set the table in a wide pan and adjust either the legs or the level of the quenchant to a height that will give a temper line where I want it. When you are ready to quench just set the piece down on the table and move back and forth and also tip it forward and back to include the tip of the blade. Then quench the rest of the blade vertically in a tank until cool enough to handle comfortably. Temper immediately.

Good luck
 
By saying "cracks where the heat was applied!" i meant when i tempered the blades i coated the edge with a nice thick coating of clay to prevent the edge over-heating (im not very good at the heat control;) ) and so by doing that the heat was applied at the top of the blade with a torch. i had normalized the one the blades once or maybe twice but i had done it so i don't think the problem lies there. But after i tempered one of the blades cracks had opened up in a nice big sun pattern about an inch in diameter which were quite obvious to the eye. The other blade had hairline cracks that could only be seen once it had been polished.:confused:
Your edge quencher seems like a nice simple way to go to get a hamon when i start to get more knives made i'll have to give that a go! :thumbup:
 
I've never had the misfortune to have a crack in a "sun pattern". Never even seen one. Are you forging your blades? If so, did you hit this one when it was too cool. I can envision radial cracks in that case. Some of the more experienced forgers will have to address this.

Also did you use "recycled" steel or new?

I haven't done it your way because of the "table" method I use gives me the results I need. But if you are going to harden the whole blade and then draw back the spine you might try the "table" but use water rather than oil to keep the edge cool while you apply heat to the spine. I guess you would still have to do an oven draw to temper the edge - you wouldn't want to leave it at totally hard. Probably better to do an oven draw and then soften the spine using the table. I haven't done it this way. Just a suggestion.
 
Well i had forged the leaf spring down in to a thinner billet but not into the blade shape. And the steel is "recycled" by the fact it was pulled of an old hardly used caravan. But these cracks only seem to appear after the temper has been given. The blade with the sun pattern cracks had been given three tempers and a normalizing after 2 of them because i had to straighten out some warps. i've heard that too many quenches stresses the steel alot?:confused:
 
I like a 220 grit finish before thermal cycles and quench. 80-120 grit can leave deep enough scratchs for a heat riser cracks to form...Ed
 
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